The present invention relates to apparatus for dressing the working surfaces of grinding wheels, particularly the working surfaces of grinding wheels in surface grinding and profile grinding machines. Still more particularly, the invention relates to dressing apparatus for numerically controlled and preferably fully automated treatment of the working surfaces of grinding wheels in grinding machines of the type wherein the holder for the grinding wheel is normally movable vertically up and down along an upright column of the frame or housing of the grinding machine and the dressing apparatus comprises several rotary dressing tools each of which is or can be designed to treat a different portion of the working surface. In such grinding machines, the dressing tools and/or the grinding wheel or wheels are normally movable relative to each other, not only in the axial direction but also radially of the grinding wheel or wheels.
It is already known to treat the working surface of the grinding wheel in a grinding machine by several tools of a dressing apparatus. For example, the grinding machine which is disclosed in U.S. Pat. No. 4,274,231 comprises a dressing apparatus with two coaxial grinding tools. The tools resemble discs which are mounted on the table of the grinding machine and are movable relative to the major part of the machine frame toward and away from positions of register with the working surface of the grinding wheel. The two dressing tools have different profiles so that each thereof can treat a differently configurated portion of the working surface. The axial spacing between the two dressing tools exceeds the axial length (thickness) of the grinding wheel. The table must be moved in parallelism with the axis of the spindle for the grinding wheel and the grinding wheel and its holder must be moved radially of the dressing tools in order to place a selected tool into material-removing engagement with a selected portion of the working surface on the grinding wheel. When the treatment of the selected portion or portions of the working surface by one of the dressing tools is completed, the table which supports the dressing tools is moved in the axial direction of the grinding wheel so as to place the other dressing tool into a position of registry with the selected portion or portions of the working surface, namely with that portion or with those portions of the working surface which cannot be properly treated, cannot be treated as satisfactorily or cannot be treated at all by the one dressing tool.
The patented grinding machine and its dressing apparatus exhibit a number of serious drawbacks. First of all, the dressing apparatus is normally located outside of the work treating area so that it occupies additional space on the base of the grinding machine. Secondly, when the need for the treatment of the working surface of a grinding wheel arises, the table with the dressing tools thereon must cover a substantial distance before the first dressing tool assumes a position in which its profile is properly positioned for treatment of one or more selected portions of the working surface of the grinding wheel. This contributes significantly to the down times of the grinding machine because each dressing operation consumes a rather long interval of time. The just described drawback of the patented grinding machine is especially serious when the grinding wheel or wheels are designed for the removal of material from bulky and heavy workpieces. An additional drawback of the patented grinding machine is that the distance between the two dressing tools exceeds the axial length of the grinding wheel so that the table which supports the dressing tools must be set in motion again when the treatment of the working surface by one of the tools is completed in order to move the other dressing tool to a position of registry with the working surface of the grinding wheel. This takes up additional amounts of time, especially since each acceleration or deceleration of the relatively heavy table takes up a reasonably long interval of time. Still another drawback of the patented apparatus is that, since the axes of the two dressing tools coincide, the versatility of the dressing apparatus is not entirely satisfactory because such mounting of the dressing tools does not permit for adequate treatment of complex or highly complex working surfaces on grinding wheels. The common axis of the dressing tools is parallel to the axis of the grinding wheel. This, too, reduces the versatility of the patented grinding machine and its dressing apparatus.